A recent, detailed study published in New Phytologist examines how understory communities in Europe have shifted over the past four decades. Some species show a clear decline, while others have expanded significantly, painting a nuanced picture of forest undergrowth changes.
Researchers led by Josep Padullés, a CREAF scientist and professor at the Autonomous University of Barcelona, find that overall plant diversity in European forests has remained stable. Yet certain groups, including Ericaceae (shrubs), Fabaceae (legumes), and Orchidaceae (orchids), have experienced higher extinction risks, while other families such as Amaranthaceae (amaranths and related crops), Cyperaceae (sedges), and Rosaceae (roses and related plants) have benefited from shifts in habitat and climate.
Analyses of evolutionary relationships show that the species in decline tend to be closely related on the plant family tree, whereas the newly increasing species come from a broader range of origins. The study highlights the important role humans have played in these slow, largely invisible changes to forest understories.
Orchids are decreasing
Species of high conservation priority, such as many orchids, are on the decline as environmental changes driven by human activity reshape their habitats. These shifts can threaten entire plant families because each family contributes uniquely to ecosystem function. The study provides a broader perspective than would be possible by examining single species alone, illustrating how different families perform distinct ecological roles and how their decline or expansion reverberates through the forest system, according to Josep Padullés, the study’s lead author and CREAF researcher.
Conversely, taller plants that require higher nitrogen levels, including some Rosaceae members and certain amaranths, have become more prevalent in temperate forests. The researchers warn that the spread of these taller species could alter forest growth patterns and overall ecosystem functioning.
To conduct the study, the team analyzed 2,672 plots across forty years, closely tracking changes in plant diversity on the ground layer of European forests.
Change through human action
The findings point to a substantial influence of human activity on understory diversity. Forest management practices and grazing—both deliberate introductions and removals—have shifted species composition in ways that can either support or hinder particular groups. These interventions have altered the balance of species, sometimes favoring grasses and sedges while limiting others, with consequences for the broader ecosystem.
Other climate-related factors, such as hotter summers or excessive nitrogen, were not the primary drivers of these changes. In fact, plant diversity rose in regions that experienced milder winters and greater rainfall, underscoring the complex interaction of multiple environmental forces.
Citation: New Phytologist study on European understory dynamics. The full reference is provided by the journal and summarized by researchers in CREAF and partner institutions.
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